What license is needed to drive ex-military vehicles in the UK?

DisclaimerI do not intend to go to the effort of actually buying a tank/ex-military vehicle, this question being inspired from watching car shows such as Top Gear in which the presenters drive a range of vehicles including past and present army vehicles.

Let’s say that I want to become a World war 2 vehicle collector. There are a range of tanks, armoured cars and other vehicles that have catapillar tracks, wheels, both (half-tracks) and most often weigh over the 3500kg that is afforded to a car license (category B). Although there are license categories that cover using vehicles with tracks and those over 3500kg, would both license categories be needed by a tank/armoured car/half-track driver in the UK?